A USB Interface ICs is an integrated circuit designed specifically for connecting a microprocessor (MPU) or microcontroller (MCU) system to a USB interface.

USB interfaces are commonly used to provide data communications and control between computers and their peripherals. They are typically very low power devices optimized for battery applications. They incorporate electrostatic discharge (ESD) protection as USB is a cabling oriented standard. 

Due to the USB interface requirements, devices can support host, device, and OTG modes of operation, but do not tend to support both Host and Device mode. Most USB interface ICs on the market today support the USB 1.1 and 2.0 standards. USB 3.0 is supported by many devices, but these have high-speed interfaces that may have additional system costs for embedded applications. USB devices typically support bus powered modes of operation and can also provide power to specification if Host or OTG compliant. This is 500mA at 5V for USB 1.x,  USB 2.0 and 900mA for USB3.x. Devices have reasonably powerful drive capability, being able to drive 5meters of cable for USB 2.0 at 480Mbits/S.

Several standards exist for USB. USB 1.1 is the oldest standard and supports bit rates up to 12Mbits/sec. USB 2.0 supports up to 480Mbits/S and USB 3.0 can support payloads up to 5Gbits/s. USB has the concept of a host and a device, and these have similar function in other bus systems to the concept of a slave and a master.  There are also USB modes like USB on the go (OTG) where the USB Devices can also act as hosts. This enables devices to interface to USB flash drives, keyboards, and similar peripherals.

The USB Interface ICs connect to the MPU system by a bus, usually parallel but for slower modes of operation this interface can be serial. Most USB2.0 and below capable chips have 8bit parallel interfaces that can also operate in 4, 2 or 1-bit modes for reasons of efficiency and flexibility. Some USB chips offer fixed conversion from and to other serial standards like SPI or I2C. They have large inbuilt FIFO buffers in both directions, and some can be found to have direct memory access (DMA) capability, allowing them to send and receive data directly from system memory. USB devices also have interrupts to the MPU to indicate that the software driver needs to take care of an issue, event or if data is available or transmission complete. Manufacturers typically provide generic driver examples for their USB Interface chips to facilitate development.

USB 3.x devices typically interface to the processor system through multiple PCI express (PCIe) serial lanes. They have inbuilt signal equalizers and may have a separate serial bus interface for control.